"Bob Eld" <nsmontassoc@[EMAIL PROTECTED]
> wrote in message
news:CrX9k.6561$L_.111@[EMAIL PROTECTED]
>
>
> Phil above has it right. That gif is a flyback design. The primary with
> the
> air gapped core forms an inductor designed to handle the DC component.
>
> Interestingly some torroids can work in this mode, most cannot. The ones
> that can have a powdered iron core. The minute spacings between the iron
> grains form the equivalent of an air gap.
>
> Again, you have to know what your core is to determine how to use it. I
> know
> you got it from a power supply but that doesn't mean much without some
> knowledge of the circuit.
>
> It is possible to measure the core if you have a scope and a few
> components
> by winding a test winding on it then measuring the B-H curve. Then, by
> applying DC, determine how the curve responds and what happens to the
> saturation characteristics.
>
> But, that's part of a course in magnetics and probably a bit beyond the
> scope of what you are trying to do.
>
> I tell you to add a capacitor to the primary to keep DC out of the core.
> That is the safest thing to do, but your drive circuit has to both
source
> and sink current. You can't do this with a single FET. You'll probably
> have
> to use a half bridge or what amounts to a two switch forward
> configuration.
>
> I think the turns ratio of 12:100 is correct. Remember you will have +/-
> 6
> volts on the primary and +/- 50 volts center taped on the secondary.
> That's
> 6:50 or 12:100, same thing.
This sounds a lot like the same project that was discussed by the OP at
length March 22 ("Need a big transformer") and March 31 ("transformers in
parallel"). If the OP simply needs +/- 24 VDC at 2 (or even 5) amps, there
are easier and better ways to get that than tinkering with parts from an
old PC power supply. Unless you need something with exotic specifications,
you can always buy it for less than you can build it (unless your time is
worth nothing or it is mostly for learning). And for learning, it is best
to build basic circuits until you understand them, and there is also a lot
you can do by just running simulations. Much better and safer than blowing
up parts in a breadboard.
I bought a 200 watt dual output +/- 43V 2A switcher originally designed
for
an audio amp for about $22 on eBay, and it is a well-made device that will
meet my needs if I ever decide to build a high-power op-amp or audio
amplifier.
Paul
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